四川盆地海相、湖相页岩气形成条件对比及开发策略

Comparative analysis of the accumulation conditions and development strategies of the marine and lacustrine shale gas from the Sichuan Basin,China

四川盆地页岩气勘探已在川东南—川南海相下志留统、川东—川东北湖相下侏罗统泥页岩层系获得了商业发现和工业气流,展示了四川盆地页岩气具有多领域、多层系、多类型的特点。采用氩离子抛光—扫描电镜、压汞—吸附联合测定、脉冲渗透率和X-射线衍射等实验测试方法,通过对海相、湖相泥页岩沉积相、生烃条件、储集特征、可压裂性和富集类型多方面对比表明,海相龙马溪组优质页岩主要发育于克拉通台内凹陷深水陆棚沉积,具有分布广,厚度稳定,有机碳含量高,有机质孔、页理、有机硅均发育的良好的生、储、可压裂一体的页岩气物质基础,3类页岩气富集类型(盆内超高压页岩气型、盆内缘超压页岩气型和盆外常压页岩气型),其中盆内超高压页岩气型和盆内缘超压页岩气型为最有利的页岩气勘探类型;湖相大安寨段有利的页岩与灰岩薄互层岩性组合,主要发育于最大湖进期碳酸盐岩湖泊的湖坡风暴滩与湖坡泥交替沉积环境,具累计厚度大,有机碳含量较高,粒缘孔缝发育,渗透性较好,钙质脆性矿物含量高的较好的生、储、可压裂近配的页岩气物质基础,是湖相有利的页岩气勘探类型。针对海、湖相不同类型页岩气的形成特点,开展适应性勘探开发技术的攻关,是实现多领域页岩气经济有效开发的关键。

Shale gas exploration in Sichuan Basin has gained great success.In south and southeast of Sichuan Province,Lower Silurian marine shale gas achieved commercial discovery,and Lower Jurassic lacustrine shale gas in east and northeast of Sichuan saw industrial gas flow.Characteristics of the shale gas in Sichuan Basin have been revealed including multi-flied,multi-layer and multi-type.Using Argon-ion polishing-SEM,MIP-adsorption analysis,pulse test and X-diffraction test,features between marine and lacustrine mud shale such as sedimentary facies,hydrocarbon generation conditions,reservoir characteristics,fracability and enrichment have been systematically investigated and compared.Results indicate that for marine facies,the high quality shales in Longmaxi Formation mainly developed at the deep-water shelf within a craton interior depression.The black shales have wide distribution,consistent thickness,high organic carbon,high organic porosity,well-developed lamellation and rich organic silicate content.All these features are favorable for marine shale gas generation,enrichment,storage,and reservoir stimulation.There are three different types in terms of shale gas enrichment （ultra-high pressure （UHP） in the basin,overpressured shale gas at the inner edge of the basin,underpressured shale gas outside the basin）.The most favorable types for shale gas exploration are intra-basin UHP and overpressured shale gas type;for lacustrine facies at Daanzhai interval,favorable lithology combination is interbedded shale and limestone which mainly developed in an alternate deposition changing between storm beach and mud of the carbonate lake slope at highest lake level.With large accumulated thickness,higher organic carbon,more grain-edge pores and fractures,high permeability and more brittle minerals （silica and calcium）,these shales are considered as potential targets for lacustrine shale gas exploration.Based on the accumulation characteristics of different shale gas types in both marine and lacustrine facies,carrying out research on adaptive exploration and development technology is the key to realize an effective and economical shale gas development in various fields.